The project is designed to help elucidate the mechanisms of renin release at a cellular and subcellular level. Studies on rat kidney slices have shown that renin release can be evoked by calcium (after a period of calcium deprivation) and by exposure to low temperature. These responses are accentuated when kidneys from animals on a low sodium diet are used. Other studies have shown that renin secretion induced by isoproterenol is inhibited by antimitotic agents and thus implicate microtubules in renin secretion. Studies on renin granules have shown that renin release from semipurified granules is inhibited by ATP. The accumulated results suggest that the underlying cellular mechanisms in renin secretion closely resemble the corresponding mechanisms in the secretion of other endocrine substances.